1. Field of the Invention
The present invention relates to a control system for the intake manifold of internal combustion engines and more particularly to a system for automatically controlling the velocity of the air-fuel mixture responsive to certain engine operation parameters. According to the present invention the length and effective cross-sectional area of the manifold runner as well as the effective plenum volume may be automatically adjusted during engine operation as a function of either the vacuum pressure level within the cylinders of the engine or engine speed. The object, of course, being to increase the velocity of the air-fuel mixture during periods of low rpms or low engine speed in order to ensure smoother and more efficient operation of the engine in terms of power and economy at lower rpms.
As will be appreciated by those skilled in the art, the intake manifold systems of internal combustion engines for passenger cars and commercial vehicles are generally designed for maximum efficiency at high or high medium engine speeds. This is a design compromise since the cross-sectional area of the intake manifold is normally fixed with no provision for adjusting the velocity of the air-fuel mixture flow at low-medium or low speeds. Consequently, most engines are markedly inefficient in terms of power and fuel consumption at low speed operation. As is also well known, the vacuum pressure within the cylinders of the engine and thus the intake manifold is inversely proportional to the speed or rpm of the engine, thus at low rpms the vacuum pressure is increased and decreases as the rpms increase. With a fixed cross-section manifold the velocity of the air-fuel mixture is thus normally decreased at low rpms. With the present invention, the length of the manifold runner and the effective cross-sectional area of the manifold runner as well as the volume of the plenum area are decreased during the high vacuum or low rpm operation. The velocity of the air-fuel mixture is thus increased so as to improve the engine operation efficiency.
2. Discussion of the Prior Art
The above discussed problems with fixed cross-section manifold runners has been long appreciated in the art and many attempts have been made to compensate for the air-fuel mixture velocity decrease during the period of high vacuum in the manifold and/or to otherwise control the mixture in the intake passages. The U.S. Patents to Loynd and Shaffer, U.S. Pat. Nos. 3,875,918 and 4,210,107 respectively are examples of devices having means for decreasing the cross-sectional area of manifold runners responsive to high vacuum pressure. The Shaffer (107) patent provides each individual fixed cross-section runner with a movable side plate controlled individually either manually or by its own vacuum motor. The movable plates of Shaffer are spring biased away from the fixed runner wall and vacuum pressure, electically or manually operated to the retracted position. The plates are mounted in and affect only one runner and hence actuators must be provided at the location of each runner. Because of the mechanics of the arrangement, the plates are limited both in their range of movement and by their ability to control only the cross-sectional area of the runners themselves. There is no control of runner length or plenum volume. the need for individual control of each runner plate also presents problems of complexity.
The Loynd patent utilizes a flexible rubber or plastic pipe section in the intake runner which assumes a restricted flow (reduced cross-section) configuration responsive to increased vacuum pressure. Although these devices provide control of the air-fuel mixture velocity, certain inherent deficiencies are present. The durability and reliability of materials such as rubber and plastics for instance are not satisfactory with extended use under engine operating conditions.
The U.S. patents to Carr and Shaffer, U.S. Pat. Nos. 4,465,035 and 4,553,507 respectively show still further examples of devices used to control the velocity of the air-fuel mixture to the cylinder intake ports. The Carr patent illustrates a form of slider valve for restricting the air flow and for imparting vortex flow at low engine speeds. Shaffer (507) provides a system of removable runner dividers with the capacity to increase or decrease the number of intake passages and hence the volume and velocity of flow to each cylinder as a solution to the common problem.
Still other approaches involve the expedient of adjusting the length of the intake manifold runner as a means to control velocity and volume of air-fuel mixture flow to the cylinders. The Gassmann U.S. Pat. No. 2,835,235 utilizes an annular intake conduit which is peripherally extended or shortened depending upon engine speed. Takeda U.S. Pat. No. 4,565,166 on the other hand utilizes an additional air intake pipe which may be selectively added to the normal intake pipe to increase the total intake runner length to obtain increased volumetric efficiency.
Another approach known to the prior art is illustrated by the Hatamura et al. U.S. Pat. No. 4,625,687 wherein the combustion chamber is provided with multiple intake ports and intake valves for controlling the supply of air-fuel mixture to the cylinders. In addition, the use of vacuum or engine speed controlled deflector plates, such as shown by the Morikawa and Knapp U.S. Pat. Nos. 4,704,996 and 4,858,567 respectively, are well known in the art. These devices are usually utilized to obtain flow characteristics such as swirl ratio or rotating flow to tailor the air-fuel mixture according to combustion parameters. Finally, the Kuehn U.S. Pat. No. 1,893,502 shows an early effort to control engine efficiency at different speeds by means of controlling the vacuum pressure in the intake manifold. This device or system was an attempt to keep the vacuum pressure in the manifold, and hence the velocity of air-fuel mixture, "balanced."